The investigators are interested in the functions of the yolk sac placenta and the chorioplacenta at various stages of gestation in the rat. In vitro techniques such as embryo culture and yolk sac culture, as well as in vivo studies, will be used to study yolk sac and placental function during the period of organogenesis as well as later in gestation. Attempts to define the alterations in embryonic nutrition in normal and pathologic states will be pursued. The unique functions of the yolk sac an chorioplacenta will be evaluated in areas of placental transport and steroid hormone synthesis and metabolism. Continued effort will be spent in determining the mechanism of action and pathologic events taking place in the rat visceral and parietal yolk sac as a result of exposure to embryotoxic agents. Studies with various teratogenic antisera will be conducted in order to study the biochemical nature of yolk sac dysfunction as produced by teratogenic antisera. Antigens from rat kidney and yolk sac which produce teratogenic antiserum will be isolated and will be used to prepare and isolate teratogenic antibodies. Subunits of teratogenic immunoglobulins will be prepared in order to determine whether they maintain their embryopathic effect. The antigenic components of the chorioplacenta will be studied in order to determine which antigens are responsible for the embryotoxic antiserum prepared with term rat placenta. Studies of yolk sac and chorioplacental function in controls and antibody treated animals will be initiated. These studies will provide the opportunity to study yolk sac and chorioplacental dysfunction during critical periods of mammalian development and focus on the nature of the endocrine, nutritional, transport and anatomical defects that may contribute to abnormal development.